1. Body Systems Interactions:
Feedback Mechanisms

2. What does it mean to keep a steady balance?
Homeostasis
All living things maintain a steady balance of water, nutrients and energy known as homeostasis.
Photo by W.J.Pilsak
What does it mean to keep a steady balance?

3. Homeostasis
The nervous and endocrine systems interact with all of the other systems to maintain homeostasis in the body.

4. Homeostasis
The pituitary gland is at the base of the hypothalamus.
Hypothalamus labeled in red.
The hypothalamus (nervous system) and the pituitary gland (endocrine system) are important in the maintenance of homeostasis.

5. Homeostasis
Homeostasis is often achieved through feedback mechanisms in the body.
Important Vocabulary
Stimulate: To make more active
Negative Feedback Loop
Inhibit: To make less active

6. Negative Feedback Loop
Homeostasis
The hypothalamus stimulates (+) the pituitary to send a hormone to a gland in the body.
That gland makes a hormone that inhibits (-) the hypothalamus and pituitary from sending the message to make more.
Negative Feedback Loop

7. A parent stimulates a child to clean their room.
Feedback Mechanisms
Parent
Child
“Clean Your Room!”
(+)
Cleans Room
(-)
Because this is complicated, we’ll use a metaphor to help us understand the process.
A parent stimulates a child to clean their room.
When the child cleans the room, it inhibits the parent from reminding the child.

8. Can you explain the shape of the line graph?
Feedback Mechanisms
Room Cleanliness
Time
This creates a feedback loop between the parent and child. While the room is not at the same level of cleanliness all of the time, it stays balanced within reasonable limits.
Can you explain the shape of the line graph?

9. Thyroxine is a hormone that increases your body’s metabolism.
The thyroid gland is stimulated to make thyroxine by a signal from the pituitary gland.
When thyroxine levels are high, it inhibits the pituitary gland from sending it’s signal.

10. Thyroxine levels in the blood
Feedback Mechanisms
Thyroxine levels in the blood
Time
This feedback mechanism keeps the amount of thyroxine hormone in the blood balanced. This allows the metabolism of the person to also stay balanced!

11. Thyroxine levels in the blood
Feedback Mechanisms
Thyroxine levels in the blood
Time
However, homeostasis CAN be disrupted. Without enough iodine in the diet, the body cannot make thyroxine.
Iodine

12. Feedback Mechanisms
The signal from the pituitary is not inhibited, and the thyroid is over-stimulated making it large and swollen.
Goiter

13. Feedback Mechanisms
Insulin and glucagon are two hormones which work together to keep a person’s blood sugar balanced.

14. When glucose levels are high, insulin is released
When glucose levels are high, insulin is released. This signals cells to absorb glucose and store it as the polysaccharide glycogen.
When glucose levels are low, glucagon is released. This signals cells to digest glycogen and release glucose into the blood.

15. Feedback Mechanisms
Blood Glucose Levels
Time
Diabetes is a disease where insulin is not produced or recognized in the body. This causes the glucose levels in the body to be too high which can cause serious problems.

16. How could these people maintain homeostasis?
Type 1 diabetes is the result of insulin producing cells in the Pancreas being destroyed.
How could these people maintain homeostasis?

17. Thermoregulation +
Warm Blood
Maintaining a steady temperature is an important aspect of homeostasis. When blood gets too warm, the hypothalamus sends a signal to glands in the skin to sweat.

18. Thermoregulation -
Cool Blood
When the blood is cooled back down, the hypothalamus sends a signal to the nerves in the sweat glands to stop sweating.

19. Fight or Flight
FEAR
STRESS
Fear and stress produce the same response in humans. This is called the fight or flight response.

20. Epinephrine (also known as adrenaline)
Fight or Flight
Epinephrine (also known as adrenaline)
Epinephrine (adrenaline) increases the heart and breathing rates while inhibiting pain receptors.
How would this response help you defend
yourself (fight) or run away (flight)?